To provide increased insight regarding the bond behavior of fiber-reinforced polymer (FRP) bars, 41 glass FRP, carbon FRP, and steel reinforced concrete beams with unconfined tension lap splices were tested. The test results are analyzed to evaluate the influence of splice length, surface deformation, modulus of elasticity, axial rigidity, and bar casting position on bond strength. Furthermore, the test results are compared with the current design expression recommended by ACI Committee 440 to evaluate its applicability. This comparison clearly indicates that the current design expression is inadequate, and that a new design equation is needed. More importantly, however, this research sheds light on the importance of the axial rigidity of the reinforcement on bond strength. Test results demonstrate that bond strength is linearly related to the axial rigidity of the reinforcement. This finding has future implications regarding the development of improved design expressions and allowing for an improved understanding of bond strength.